1. Field of the Invention
The present invention relates to a pellicle for lithography. More particularly, the present invention relates to a pellicle suitable for lithography using extreme ultra violet (EUV) light, and a method for producing the same.
2. Description of the Related Art
With high integration of semiconductor devices, patterns formed by lithography are microminiaturized, and currently devices having a pattern width of about 45 nm are being put to practical use. Such a narrow line pattern can be realized by lithography based on a manner such as an ArF immersion method and a double exposure method which are improved techniques of conventional excimer exposure technologies.
However, in such lithography based on the excimer exposure technologies, it is regarded as difficult to meet patterning requiring further miniaturization with a pattern width of 32 nm or less. Therefore, lithography using extreme ultra violet (EUV) light has attracted attention as a new exposure technology to replace the lithography based on the excimer exposure technologies.
To put to practical use an exposure technology using EUV light having a dominant wavelength of 13.5 nm, it is indispensable to develop not only a light source, but also a new resist, a pellicle, and the like. Among these, development for the light source and resist has been already made substantial progress, whereas for pellicle, many technical problems which have to be solved for realization of a pellicle for EUV remain unsolved.
A pellicle film provided in a pellicle for EUV requires not only a dust-proof function for preventing adherence of foreign matters on a photomask, but also high transmission for EUV light and chemical stability. However, the prospects for resolution of problems of such high transmission and chemical stability, and further the material development for a practical pellicle film having an excellent fabrication yield are still far from certain at present.
Although a transparent material for light in a wavelength range having a dominant wavelength of 13.5 nm is currently not known, silicon has relative high transmittance for the light having such a wavelength, and therefore silicon has attracted attention as a pellicle film material for EUV. As regards this, for example, see Shroff et al. “EUV pellicle Development for Mask Defect Control,” Emerging Lithographic Technologies X, Proc of SPIE Vol. 6151 615104-1 (2006) (Non-Patent Document 1) and U.S. Pat. No. 6,623,893 (Patent Document 1).
However, silicon used as a pellicle film in Non-Patent Document 1 is a film deposited by a sputtering method or the like, and therefore necessarily become amorphous, inevitably resulting in the high absorption coefficient and low transmittance in the EUV region.
Although a pellicle film disclosed in Patent Document 1 is also made of silicon, this silicon film is premised on a deposition by CVD method or the like. In this case, the silicon film results in an amorphous or polycrystalline film, and therefore the absorption coefficient in the EUV region inevitably have a high value.
In addition, there are also the following problems: as the pellicle films disclosed in Patent Document 1 and Non-Patent Document 1, a strong stress is easily introduced into a silicon crystal formed by a sputtering or CVD methods, and the above stress easily results in deteriorated and uneven optical film properties.
Thus, the inventors solved the above shortcomings, invented a practical pellicle for EUV having high transmission and excellent chemical stability and a method for producing the same, and then filed an application (Japanese Patent Application No. 2007-293692 (unpublished)).
However, the result of a subsequent further study found the following problems: in the case where a silicon single crystal film having a (100) plane as its principal plane is used as a pellicle film in the invention according to the above patent application, the EUV pellicle has an excellent optical property, and however a crack or defect tends to occur in the silicon crystal film in steps of stripping, etching, handling, and the like when a silicon crystal is made into a thin film in a pellicle production process, thereby decreasing a fabrication yield. For this reason, the inventors further improve the invention according to the above patent application, and then filed a new patent application (Japanese Patent Application No. 2008-120664 (unpublished)).
A subsequent study by the inventors found that this improvement invention also still has the following drawbacks: edge chipping occurs due to vibrations during transportation or the like; the temperature of its silicon single crystal film increases due to the light energy during EUV exposure, so that a pellicle frame attached by an adhesive tends to cause warpage under thermal stress due to the difference in the rate of thermal expansion, cause distortion during adhering, or the like. Then, the inventors made a study to further improve it, and then reach to the present invention.
The meaning of signs used to represent a crystal plane and its orientation herein is described in, for example, Fumio, Shimura “Semiconductor Silicon Crystal Technology” Chapter 2, Paragraph 2.2, (Maruzen Co., Ltd. (1993): Non-Patent Document 2), which is generally used by those skilled in the art.